CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Beginning Balance at Dec. 31, 2018	$ 7,157,000	$ 2,000	$ 243,022,000	$ (235,867,000)
Beginning Balance, shares at Dec. 31, 2018		2,148
Issuance of common stock under stock plans, net	(4,000)		(4,000)
Issuance of common stock under stock plans, net, shares		31
Stock-based compensation	263,000		263,000
Net loss	(2,580,000)			(2,580,000)
Ending Balance at Dec. 31, 2019	$ 4,836,000	$ 2,000	243,281,000	(238,447,000)
Ending Balance, shares at Dec. 31, 2019	2,179	2,179
Issuance of common stock under stock plans, net	$ (2,000)		(2,000)
Issuance of common stock under stock plans, net, shares		41
Exercise of pre-funded warrants	2,000		2,000
Exercise of pre-funded warrants, shares		116
Sale of common stock, net of financing	1,619,000	$ 1,000	1,618,000
Sale of common stock, net of financing, shares		1,218
Deemed dividend for warrant exercise price adjustment	392,000		392,000	(392,000)
Stock-based compensation	257,000		257,000
Net loss	(3,780,000)			(3,780,000)
Ending Balance at Dec. 31, 2020	$ 2,932,000	$ 3,000	$ 245,548,000	$ (242,619,000)
Ending Balance, shares at Dec. 31, 2020	3,554	3,554